E-field-modulated bistable molecular mechanical device

ABSTRACT

A molecular system is provided for nanometer-scale reversible electronic and optical switches, specifically, electric field-activated molecular switches that have an electric field induced band gap change that occurs via rotation of rotor units connected to immobile stator units. The molecular system has two branches on one side of an immobile junction unit and one or two branches on the opposite side to thereby provide “Y” and “X” configurations, respectively. The ends of the branches opposite the junction unit are connected to, or electrically associated with, other molecular systems or substrates, such as electrodes. The rotor units each rotate between two states as a function of an externally-applied field. Both multi-stable molecular mechanical devices and electric field-activated optical switches are provided.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a continuation-in-part of application Ser.No. 10/013,643, filed Nov. 13, 2001 now U.S. Pat. No. 6,751,365, whichis a continuation-in-part application of application Ser. No.09/898,799, filed Jul. 3, 2001 now pending, which is acontinuation-in-part application of Ser. No. 09/844,862, filed Apr. 27,2001 now U.S. Pat. No. 6,763,158, which in turn is acontinuation-in-part application of Ser. No. 09/823,195, filed Mar. 29,2001 now pending, which in turn is a continuation-in-part application ofSer. No. 09/759,438, filed Jan. 12, 2001, now U.S. Pat. No. 6,512,119,issued Jan. 28, 2003, which in turn is a continuation-in-partapplication of Ser. No. 09/738,793, filed Dec. 14, 2000, now U.S. Pat.No. 6,663,797, issued Dec. 16, 2003.

The present application is directed to a specific molecular system thatinvolves at least two rotatable segments (rotors) that have a largedipole moment and that each link with two other portions of the moleculethat are immobilized (stators). The molecular system disclosed hereinprovides switching from one state to a different state, characterized bya change in the electronic properties and/or the optical properties ofthe molecules.

TECHNICAL FIELD

The present invention relates generally to electronic and opticaldevices whose functional length scales are measured in nanometers, and,more particularly, to classes of molecules that provide electronic andoptical switching. Electronic and optical devices both of micrometer andnanometer scale may be constructed in accordance with the teachingsherein.

BACKGROUND ART

The area of molecular electronics is in its infancy. To date, there havebeen two convincing demonstrations of molecules as electronic switchespublished in the technical literature; see, C. P. Collier et al.,Science, Vol. 285, pp. 391-394 (16 Jul. 1999) and C. P. Collier et al.,Science, Vol. 289, pp. 1172-1175 (18 Aug. 2000), but there is a greatdeal of speculation and interest within the scientific communitysurrounding this topic. In the published work, a molecule called arotaxane or a catenane was trapped between two metal electrodes andcaused to switch from an ON state to an OFF state by the application ofa positive bias across the molecule. The ON and OFF states differed inresistivity by about a factor of 100 and 5, respectively, for therotaxane and catenane.

The primary problem with the rotaxane was that it is an irreversibleswitch. It could only be toggled once. Thus, it can be used in aprogrammable read-only memory (PROM), but not in a ROM-like device norin a reconfigurable system, such as a defect-tolerant communications andlogic network. In addition, the rotaxane requires an oxidation and/orreduction reaction to occur before the switch can be toggled. Thisrequires the expenditure of a significant amount of energy to toggle theswitch. In addition, the large and complex nature of rotaxanes andrelated compounds potentially makes the switching times of the moleculesslow. The primary problems with the catenanes are small ON-to-OFF ratioand a slow switching time.

Thus, what is needed is a molecular system that avoids chemicaloxidation and/or reduction, permits reasonably rapid switching from afirst state to a second, is reversible to permit the fabrication ofROM-like devices, and can be used in a variety of electronic and/oroptical devices.

DISCLOSURE OF INVENTION

In accordance with the present teachings, a molecular system having atleast three branches is provided, with one end of each branch connectedto an immobile junction unit, with two of the branches on one side ofthe junction unit and with at least one other branch on the oppositeside of the junction unit, wherein either:

-   -   the molecular system comprises three branches, wherein the two        branches each contain an immobile stator unit in its backbone,        and the two branches each further contain at least one rotatable        rotor unit in its backbone between the stator unit and the        junction unit; or    -   the molecular system comprises four branches, with two of the        branches on one side of the junction unit and with two other        branches on the opposite side thereof wherein each branch        contains contain an immobile stator unit in its backbone, and        each branch further contain at least one rotatable rotor unit in        its backbone between the stator unit and the junction unit,        wherein each rotor unit rotates between two states as a function        of an externally-applied field.

Further in accordance with the present teachings, a multi-stablemolecular mechanical device is provided, comprising a molecular systemconfigured within an electric field generated by a pair of electrodesand electrically connected thereto. The molecular system is as describedabove, wherein each rotor portion rotates with respect to its associatedstator portions between at least two different states upon applicationof the electric field, thereby inducing a band gap change in themolecular system, wherein in a first state, there is extendedconjugation over at least most of the molecular system, resulting in arelatively smaller band gap, and wherein in a second state, the extendedconjugation is changed, resulting in a relatively larger band gap, andwherein in intermediate states, the conjugation is intermediate betweenthat of the first state and that of the second state.

Still further in accordance with the teachings herein, an electricfield-activated optical switch is provided, comprising a molecularsystem configured within an electric field generated by a pair ofelectrodes. The molecular system is as described above, wherein eachrotor portion rotates with respect to its associated stator portionsbetween at least two different states upon application of the electricfield, thereby inducing a band gap change in the molecular system,wherein in a first state, there is extended conjugation over at leastmost of the molecular system, resulting in a relatively smaller bandgap, wherein in a second state, the extended conjugation is changed,resulting in a relatively larger band gap, and wherein in anintermediate state, the conjugation is intermediate between that of thefirst state and that of the second state.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 a is a schematic representation of two crossed wires, with atleast one molecule at the intersection of the two wires;

FIG. 1 b is a perspective elevational view, depicting the device shownin FIG. 1 a;

FIG. 2 is a schematic representation of a two-dimensional array ofswitches of the present invention, depicting a 6×6 crossbar switch;

FIG. 3 is a schematic representation (perspective, transparent view) ofa two color (e.g., black and white) display screen construction for usein accordance with the present invention;

FIG. 3 a is a detail for a colorant layer element of the display screendepicted in FIG. 3;

FIG. 4 is a schematic representation (perspective, transparent view) ofa full-color display screen construction for use in accordance with thepresent invention;

FIG. 5 is a schematic representation of a scan addressing embodiment ofa two-color display screen construction for use in accordance with thepresent invention;

FIG. 6 is a schematic model depicting an E-field-induced band gap changevia molecular conformation change (rotor/stator type of model);

FIG. 7 is a schematic model, similar to FIG. 6, but depicting a “Y”configuration having a rotor unit in each of two branches; and

FIG. 8 is a schematic model similar to FIG. 7, but depicting an “X”configuration having a rotor unit in each of four branches.

BEST MODES FOR CARRYING OUT THE INVENTION

Definitions:

The term “self-assembled” as used herein refers to a system thatnaturally adopts some geometric pattern because of the identity of thecomponents of the system; the system achieves at least a local minimumin its energy by adopting this configuration.

The term “singly configurable” means that a switch can change its stateonly once via an irreversible process such as an oxidation or reductionreaction; such a switch can be the basis of a programmable read-onlymemory (PROM), for example.

The term “reconfigurable” means that a switch can change its statemultiple times via a reversible process such as an oxidation orreduction; in other words, the switch can be opened and closed multipletimes, such as the memory bits in a random access memory (RAM) or acolor pixel in a display.

The term “bi-stable” as applied to a molecule means a molecule havingtwo relatively low energy states separated by an energy (or activation)barrier. The molecule may be either irreversibly switched from one stateto the other (singly configurable) or reversibly switched from one stateto the other (reconfigurable).

Micron-scale dimensions refers to dimensions that range from 1micrometer to a few micrometers in size.

Sub-micron scale dimensions refers to dimensions that range from 1micrometer down to 0.05 micrometers.

Nanometer scale dimensions refers to dimensions that range from 0.1nanometers to 50 nanometers (0.05 micrometers).

Micron-scale and submicron-scale wires refers to rod or ribbon-shapedconductors or semiconductors with widths or diameters having thedimensions of 0.05 to 10 micrometers, heights that can range from a fewtens of nanometers to a micrometer, and lengths of several micrometersand longer.

“HOMO” is the common chemical acronym for “highest occupied molecularorbital”, while “LUMO” is the common chemical acronym for “lowestunoccupied molecular orbital”. HOMOs and LUMOs are responsible forelectronic conduction in molecules and the energy difference between theHOMO and LUMO and other energetically nearby molecular orbitals isresponsible for the color of the molecule.

An optical switch, in the context of the present invention, involveschanges in the electro-magnetic properties of the molecules, both withinand outside that detectable by the human eye, e.g., ranging from the farinfra-red (IR) to deep ultraviolet (UV). Optical switching includeschanges in properties such as absorption, reflection, refraction,diffraction, and diffuse scattering of electromagnetic radiation.

The term “transparency” is defined within the visible spectrum to meanthat optically, light passing through the colorant is not impeded oraltered except in the region in which the colorant spectrally absorbs.For example, if the molecular colorant does not absorb in the visiblespectrum, then the colorant will appear to have water cleartransparency.

The term “omni-ambient illumination viewability” is defined herein asthe viewability under any ambient illumination condition to which theeye is responsive.

Basic Information on Prior Art Crossed Wire Switches:

The essential device features are shown in FIGS. 1 a-1 b and arediscussed in greater detail in the above-related patent applications andpatent. A crossed wire switch 10 comprises two wires 12, 14, each eithera metal or semiconductor wire, that are crossed at some non-zero angle.In between those wires is a layer of molecules or molecular compounds16, denoted R in FIGS. 1 a and 1 b. The particular molecules 18 (denotedR_(S)) that are sandwiched at the intersection of the two wires 12, 14are identified as switch molecules, also interchangeable referred toherein as a junction. When an appropriate voltage is applied across thewires, the switch molecules are either oxidized or reduced. When amolecule is oxidized (reduced), then a second species is reduced(oxidized) so that charge is balanced. These two species are then calleda redox pair. One example of this device would be for one molecule to bereduced, and then a second molecule (the other half of the redox pair)is oxidized. In another example, a molecule is reduced, and one of thewires is oxidized. In a third example, a molecule is oxidized, and oneof the wires is reduced. In a fourth example, one wire is oxidized, andan oxide associated with the other wire is reduced. In all cases,oxidation or reduction will affect the tunneling distance or thetunneling barrier height between the two wires, thereby exponentiallyaltering the rate of charge transport across the wire junction, andserving as the basis for a switch.

The electrical tasks performed by these devices are largely determinedby the types of wires (electrodes) and the interwire materials that areused. Table I presents the various types of devices that might befabricated from various combinations of the wires 12, 14 in FIGS. 1 a-1b.

TABLE I Wire (Electrode) Materials Semicon- ductor- Semicon-Semiconductor- Metal- Metal- Metal- ductor semiconductor Device metalmetal semicon- (p-n (hetero- Type (same) (different) ductor junction)junction) Resistor X X X Tunneling X X X resistor Resonant X X Xtunneling resistor Diode X X X X Tunneling X X X X diode Resonant X X XX tunneling diode Battery X X X

Depending on the molecules or materials that are used between the wires(the electrodes), each junction can either display the types ofelectrical function described below immediately on contact of the wiresor the junction can have a switching function that acts to connect ordisconnect the two wires together electrically. This switch can eitherbe singly configurable or reconfigurable. In the first case, the initialstate of the switch is open or closed. In the second case, by cyclingthe polarity and magnitude of the voltage on the switch beyond theappropriate threshold values, it is possible to reversibly oxidize orreduce the properly selected materials or molecules to close or open theswitch many times. In either case, when closed, the type of electricalconnection that is made between the wires depends upon the materialsfrom which the wires (or electrodes) are fabricated as well as theidentity of the molecules or materials between the wires.

Table I above shows a matrix of the various types of functions that canbe obtained from various combinations of electrode materials andmaterials or molecules used in the junction. A resistor has a linearcurrent-voltage characteristic, and is made by intentionallyover-reducing the junction between various types of wires to essentiallyform a short circuit between the wires. The opposite of this process isto over-oxidize a junction, which will consume the wire in a localizedregion and effectively break the wire (create an open circuit) in thatwire at the position of the junction. A tunneling resistor maintains athin, approximately 2 nanometer thick, insulating barrier between wiresand has an exponential current-voltage characteristic. In the case thatjunction molecules or materials have a sharply defined energy stateinside the band gap of an electrically insulating barrier that can beaccessed by electrically biasing the junction, the connection betweenthe wires can exhibit a flow of electrical current that is dominated bythe process of resonant tunneling. The resonant tunneling can produceone or more inflection points in the otherwise exponentialcurrent-voltage characteristic of a tunneling resistor. A diode is ajunction that passes current more easily in one direction than in theother, and thus has an asymmetry in the current-voltage characteristicfor positive and negative voltages. A tunneling diode has both thepositive-negative voltage asymmetry of the diode and the exponentialcurrent-voltage characteristic of the tunneling resistor. A resonanttunneling diode has a positive-negative voltage asymmetry plus it has apeak in its current-voltage characteristic, such that over a restrictedrange of increasing magnitude of the voltage the magnitude of thecurrent actually decreases, a phenomenon that is known as negativedifferential resistivity. In general, any real junction between wiresformed by the processes described above will actually have two or moreof the electrical functions described, with the effective circuitelements connected in series.

Thus, the present invention may be executed with any number of metallicor semiconducting wire/molecule combinations, depending on the deviceproperties desired from the assembled circuit.

Basic Information on Prior Art Fabrication of Wire Electrodes

Process-Defined Wires (defined as wires that are prepared byconventional electronic-circuit processing techniques; wires aretypically prepared on a substrate as part of a circuit):

Metallic and semiconductor wires, with diameters ranging from severalmicrometers to a single micrometer (defined as micrometer-scale), orwith diameters ranging from a single micrometer down to 40 nanometers(defined as sub-micrometer scale) in diameter, may be prepared usingwell-established art, including lithographic (optical, ultraviolet, orelectron beam) technologies. These wires normally have a ribbon shape orrectangular cross section, although circular cross sections are notprecluded, with the width of the wire being determined by thelithographic process used to define the wire and its height beingdefined by the amount of material deposited in the region defined bylithography.

Chemically-Prepared Wires (these wires are prepared by techniques otherthan conventional electronic processing technology; wires are typicallyprepared as a bulk material, rather than as part of a circuit board):

Metal and semiconductor nanowires are defined as wires with diametersbelow 50 nanometers (typically 2 to 20 nanometers), and with lengths inthe range of 0.1 micrometers to 50 micrometers (typically 5 to 10micrometers). These may be prepared chemically using any one of a numberof techniques described in the references given below.

One example of a reported technique for the production of semiconductornanowires of the semiconducting element germanium is to react germaniumtetrachloride and phenyl germanium(IV) chloride with a dispersion ofsodium metal in the solvent toluene, and at a temperature near 300° C.in a closed vessel, under an inert environment, for a period of severaldays. That preparation produces single-crystal germanium nanowires ofdiameters three to thirty nanometers, and of lengths from 0.5 to 10micrometers.

A second example of a reported technique for the production ofsemiconductor nanowires of the semiconducting element silicon, is tolaser vaporize a target containing elemental silicon and iron. Thetarget is placed in a vacuum oven at 1300° C., and an inert gas isflowed through the oven during the vaporization process. This techniqueproduces silicon wires that have diameters in the range of 20 to 30nanometers, and lengths ranging from 1 to 20 micrometers.

One example of a reported technique for the production of metallicnanowires of the metallic element gold is to electrochemically grow goldwires within the pores of an anodically etched aluminum oxide thin film.The aluminum oxide is dissolved in acidic solution, releasing the goldnanowires, which are then collected. Gold nanowires grown in this mannerare characterized by diameters ranging from 20 to 30 nanometers, andlengths ranging from 0.5 to 5 micrometers.

Nanowires of various metallic and semiconducting materials may beprepared in a variety of fashions. Some of these devices will requiredoped semiconductor wires, such as doped Si.

For the case of Si wires, the wires can be doped when the wires arephysically prepared. In this case, it is necessary to add the dopantinto the reaction vessel as the wires are formed. For example, in thelaser ablation/vacuum oven preparation technique described above, asmall amount of dopant gas, such as phosphine (PH₃) or arsenic(III)hydride (AsH₃) is added into the inert gas (argon, for example) thatflows through the vacuum oven during the laser ablation/wire formationprocess.

Conversely, these wires can be modulation-doped by coating theirsurfaces with appropriate molecules—either electron-withdrawing groups(Lewis acids, such as boron trifluoride (BF₃)) or electron-donatinggroups (Lewis bases, such as alkyl amines) to make them p-type or n-typeconductors, respectively. See wire preparation routes listed below. FIG.1 b depicts a coating 20 on wire 12 and a coating 22 on wire 14. Thecoatings 20, 22 may be modulation-doping coatings, tunneling barriers(e.g., oxides), or other nano-scale functionally suitable materials.Alternatively, the wires 12, 14 themselves may be coated with one ormore R species 16, and where the wires cross, R_(s) 18 is formed. Or yetalternatively, the wires 12, 14 may be coated with molecular species 20,22, respectively, for example, that enable one or both wires to besuspended to form colloidal suspensions, as discussed below.

To dope the wires via modulation doping, it is necessary to chemicallyfunctionalize the surface of the wires using organic or inorganicmolecules that will covalently bind to the Si—O—H groups at the surfaceof the wires. When silicon nanowires are exposed to air, a thin surfacelayer (1 nm) of SiO₂ will naturally form, and at the SiO₂/air interface,the SiO₂ surface is terminated by Si—O—H bonds. Groups that will bind toor replace Si—O—H groups are not limited to but includeR—Si(CH₃)_(x)(OCH_(3-x)), R—Si(CH₃)_(x)(OCH₂CH_(3-x)),R—Si(CH₃)_(x)Cl_(3-x), and others. In this case, R represents an organicor inorganic moiety that can contain electron-withdrawing (a Lewis acid)or electron-donating groups (a Lewis base). This chemistry of bindingmolecules to a SiO₂ passivated silicon surface is well established. Onepublished example reaction for binding molecules to the surface of SiO₂passivated silicon is:Si—O—H_((surface))+R—Si(CH₃)₂Cl→Si—O—Si(CH₃)₂R+HCl

Other semiconductor wires can be functionalized with organoamines,organo-thiols, organo-phosphates, etc.

Semiconductor nanowires have been modulation-doped (i.e., as indicatedby a change in conductivity of silicon nanowires when compounds adsorbon the wires); see, e.g., Yi Cui et al, “Doping and Electrical Transportin Silicon Nanowires”, The Journal of Physical Chemistry B, Vol. 104,No. 22, pp. 5213-5216 (Jun. 8, 2000); Yi Cui et al, “FunctionalNanoscale Electronic Devices Assembled Using Silicon Nanowire BuildingBlocks”, Science, Vol. 291, pp. 851-852 (2 Feb. 2001); and Yi Cui et al,“Nanowire Nanosensors for Highly Sensitive and Selective Detection ofBiological and Chemical Species”, Science, Vol. 293, pp. 1289-1292 (17Aug. 2001).

For the case of other nanowires, such as metal nanowires, the wires canbe chemically functionalized with R—SH (for gold or silver wires), orR—NH₂ (for platinum wires and palladium wires), or R—CO₂H for othermetals such as Al₂O₃-coated aluminum wires or titanium wires), where theR-group denotes some organic moiety that will lend the wire certainchemical properties—such as the property that will allow the personskilled in the art to disperse the wires, as a colloid, in a solvent. Inone example, gold wires might be functionalized with dodecanethiol(C₁₂H₂₅SH). The dodecanethiol not only will provide the wires with athin surface tunneling barrier, but will also allow for the wires to bedispersed in simple organic solvents, such as hexane or chloroform.

Basic Information on Prior Art Wire Preparation Routes

The following materials may be prepared as nanowires according to thereference listed.

Silicon: A. M. Morales et al, “A laser ablation method for the synthesisof crystalline semiconductor nanowires”, Science, Vol. 279, pp. 208-211(Jan. 9, 1998).

Germanium: J. R. Heath et al, “A liquid solution synthesis of singlecrystal germanium quantum wires”, Chemical Physics Letters, Vol. 208,pp. 263-268 (Jun. 11, 1993).

Metal Nanowires: V. P. Menon et al, “Fabrication and Evaluation ofNano-electrode Ensembles”, Analytical Chemistry, Vol. 67, pp. 1920-1928(Jul. 1, 1995).

Functionalizing Silicon: T. Vossmeyer et al, “Combinatorial approachestoward patterning nanocrystals”, Journal of Applied Physics, Vol. 84,pp. 3664-3670 (Oct. 1, 1998) (one of a number of references).

Functionalizing the Surfaces of Gold Nanostructures: D. V. Leff et al,“Thermodynamic Size Control of Au Nanocrystals: Experiment and Theory”,The Journal of Physical Chemistry, Vol. 99, p. 7036-7041 (May 4, 1995).

Molecular switching components may come from any number of differentclasses of molecules, depending, again, on the desired properties of thedevice. The key requirement of the molecules is that, when they aresandwiched between two wires, they may be electrochemically modified(i.e. oxidized or reduced) by applying a voltage across the wires. Whenthe molecular components are so modified, the net effect is that thetunneling barrier between the two wires is modified, and the rate ofcurrent flow is changed. This forms the basis of a switch that can, inturn, be used for memory, logic operations, and communication and signalrouting networks. Molecular switches can include redox pairs ofmolecules, in which application of a voltage reduces one of themolecules and oxidizes the other. An example of such a molecular redoxpair might be: nickelocene (dicyclopentadienyl nickel), or Cp₂Ni, withtetrabutyl ammonium hexafluorophosphate (Bu₄NPF₆). The reaction, then,would be:(reduction) Cp₂Ni+Bu₄NPF₆→Cp₂Ni⁻+Bu₄NPF₆ ⁺ (−1.7 V)or(oxidation) Cp₂Ni+Bu₄NPF₆→Cp₂Ni⁺+Bu₄NPF₆ ⁻ (−0.1 V)

The nickelocene system is of particular interest in that the reduction,as probed by solution phase cyclic voltammetry, is highly asymmetric.Such asymmetry is analogous to magnetization hysteresis curves that formthe basis for stable and rewriteable magnetic memory. However, in thepresence of oxygen, the reduction of nickelocene is irreversible, asprobed by solution phase voltammetry. In either case, reduction oroxidation of this system will modify the tunneling barrier between thetwo wires between which the molecules are sandwiched. Thus, this systemcould operate as either a reconfigurable, or a singly configurablemolecular switch. For metallocene systems, see, e.g., J. D. L. Hollowayet al, “Electron-transfer reactions of metallocenes: Influence of metaloxidation state on structure and reactivity”, Journal of the AmericanChemical Society, Vol. 101, pp. 2038-2044 (Apr. 11, 1979).

The connector species 16 comprises a material that displays asignificant, or measurable, hysteresis in its current-voltage curve,obtained either from solution electrochemistry or from current-voltagecharacteristics in a solid-state junction. Examples of such speciesinclude metallocenes, rotaxanes, pseudo-rotaxanes, and catenanes, whichrely on intramolecular hydrogen bonding. While such molecules are usefulfor the purpose disclosed, however, simple intramolecular hydrogenbonding forces are relatively easily exceeded under certain conditions,as discussed above.

As illustrated in FIG. 2, the switch 10 can be replicated in atwo-dimensional array to form a plurality, or array, 60 of switches toform a crossbar switch. FIG. 2 depicts a 6×6 array 60, but the inventionis not so limited to the particular number of elements, or switches, inthe array. Access to a single point, e.g., 2 b, is done by impressingvoltage on wires 2 and b to cause a change in the state of the molecularspecies 18 at the junction thereof, as described above. Thus, access toeach junction is readily available for configuring only thosepre-selected junctions in accordance with the teachings herein. Detailsof the operation of the crossbar switch array 60 are further discussedin above-referenced U.S. Pat. No. 6,128,214.

Optical Switches

Optical switches are described in greater detail in co-pending U.S.application Ser. No. 09/981,166, filed on Oct. 16, 2001. A genericexample taken from that application is depicted herein in FIG. 3,wherein a display screen 300 is shown that incorporates at least onecolorant layer 301. The colorant layer 301 comprises a pixel array usingelectrical field switchable, reconfigurable, dye or pigment molecules ofthe present invention, described in greater detail below and genericallyreferred to as a “molecular colorant”. Each dye or pigment molecule isfield switchable either between an image color (e.g., black) andtransparent or between two different colors (e.g., red and green).

Referring briefly to FIG. 3 a, the colorant layer 301 is an addressablepixel array formed of bi-stable molecules arrayed such that a selectedset of molecules correlates to one pixel. The colorant layer 301 is athin layer coated on a background substrate 303 having the display'sintended background color (e.g., white). The substrate 303 may comprise,for example, a high dielectric pigment (e.g., titania) in a polymerbinder that provides good white color and opacity while also minimizingthe voltage drop across the layer. The stratified combination ofcolorant layer 301 and substrate 303 thus is fully analogous to a layerof ink on paper. In a blank mode, or erased state, each molecule isswitched to its transparent orientation; the “layer of ink” isinvisible. The background (e.g., white pixels) shows through in thosepixel areas where the colorant layer 301 molecules are switched to thetransparent orientation. A transparent view-through layer 305, such asof a clear plastic or glass, is provided superjacent to thecolorant-background sandwich to provide appropriate protection. Theview-through layer 305 has a transparent electrode array 307 for pixelcolumn or row activation mounted thereto and positioned superjacently tothe colorant layer 301. The background substrate 303 has a complementaryelectrode array 309 for pixel row or column activation mounted thereto(it will be recognized by those skilled in the art that a specificimplementation of the stratification of the electrode arrays 307, 309for matrix addressing and field writing of the individual pixels mayvary in accordance with conventional electrical engineering practices).Optionally, the pixels are sandwiched by employing thin film transistor(TFT) driver technology as would be known in the art.

The present display 300 is capable of the same contrast and color ashard copy print. A molecular colorant is ideal because its size and massare infinitesimally small, allowing resolution and colorant switchingtimes that are limited only by the field writing electrodes andcircuitry. Like ink, the colorant layer 301 may develop adequate densityin a sub-micron to micron thin layer, potentially lowering the fieldvoltage required to switch the colorant between logic states and thusallowing the use of inexpensive drive circuitry.

Suitable reconfigurable bi-stable and multi-stable molecules for use insuch displays are disclosed below and claimed herein. In the main, thesemolecules have optical properties (e.g., color) that are determined bythe extent of their π orbital electron conjugation. The opticalproperties, including color or transparency, of the molecule change withfield polarity applied across the molecule and remains chromaticallystable in the absence of an applied electric field. By disrupting thecontinuity of conjugation across a molecule, the molecule may be changedfrom one optical state to another, e.g., colored to transparent or onecolor to another color. Electric dipoles may be designed into thecolorant that can physically cause this disruption by rotating orotherwise distorting certain segments of the dye or pigment moleculerelative to other segments, when an external electric field is appliedor changed.

The colorant layer 301 is a homogeneous layer of molecules which arepreferably colored (e.g., black, cyan, magenta, or yellow) in amore-conjugated orientation and transparent in a less-conjugatedorientation. By making the abutting background substrate 303 white, thecolorant layer 301 may thereby produce high contrast black and white,and colored images. The colorant layer 301 may comprise a single fieldswitchable dye or pigment or may comprise a mixture of differentswitchable dyes or pigments that collectively produce a composite color(e.g., black). By using a molecular colorant, the resolution of theproduced image is limited only by the electric field resolution producedby the electrode array 307, 309. The molecular colorant additionally hasvirtually instantaneous switching speed, beneficial to the needs of fastscanning (as described with respect to FIG. 5 hereinafter). In certaincases, the molecular colorant may be contained in a polymeric layer.Polymers for producing such coatings are well known, and include, forexample, acrylates, urethanes, and the like. Alternatively, the colorantlayer 301 may be self-assembled.

In one embodiment, the colorant layer 301 is offered as a substitute formatrix-addressed liquid crystal flat panel displays. As is well knownfor such displays, each pixel is addressed through rows and columns offixed-position electrode arrays, e.g., 307, 309. The fixed-positionelectrode arrays 307, 309 consist of conventional crossbar electrodes311, 313 that sandwich the colorant layer 301 to form an overlappinggrid (matrix) of pixels, each pixel being addressed at the point ofelectrode overlap. The crossbar electrodes 311, 313 comprise parallel,spaced electrode lines arranged in electrode rows and columns, where therow and column electrodes are separated on opposing sides of thecolorant layer 301. Preferably, a first set of transparent crossbarelectrodes 307 (401, 402 in FIG. 4 described in detail hereinafter) isformed by thin film deposition of indium tin oxide (ITO) on atransparent substrate (e.g., glass). These row addressable pixelcrossbar electrodes 307 are formed in the ITO layer using conventionalthin film patterning and etching techniques. The colorant layer 301 andbackground substrate 303 are sequentially coated over or mounted to thetransparent electrode layer, using conventional thin film techniques(e.g., vapor deposition) or thick film techniques (e.g., silkscreen,spin cast, or the like). Additional coating techniques includeLangmuir-Blodgett deposition and self-assembled monolayers. Columnaddressable pixel crossbar electrodes 309 (402, 404 in FIG. 4) arepreferably constructed in like manner to the row electrodes 307. Thecolumn addressable pixel crossbar electrodes 309 may optionally beconstructed on a separate substrate that is subsequently adhered to thewhite coating using conventional techniques.

This display 300, 400 provides print-on-paper-like contrast, color,viewing angle, and omni-ambient illumination viewability by eliminationof the polarization layers required for known liquid crystal colorants.Using the described-display also allows a significant reduction in powerdrain. Whereas liquid crystals require a holding field even for a staticimage, the present molecules of the colorant layer 301 can be modal inthe absence of a field when bi-stable molecules are used. Thus, thepresent bi-stable colorant layer 301 only requires a field when a pixelis changed and only for that pixel. The power and image qualityimprovements will provide significant benefit in battery life anddisplay readability, under a wider range of viewing and illuminationconditions for appliances (e.g., wristwatches, calculators, cell phones,or other mobile electronic applications) television monitors andcomputer displays. Furthermore, the colorant layer may comprise a mosaicof colored pixels using an array of bi-stable color molecules of variouscolors for lower resolution color displays.

Since each colorant molecule in colorant layer 301 is transparentoutside of the colorant absorption band, then multiple colorant layersmay be superimposed and separately addressed to produce higherresolution color displays than currently available. FIG. 4 is aschematic illustration of this second embodiment. A high resolution,full color, matrix addressable, display screen 400 comprises alternatinglayers of transparent electrodes—row electrodes 401, 403 and columnelectrodes 402 and 404—and a plurality of colorant layers 405, 407, 409,each having a different color molecule array. Since each pixel in eachcolorant layer may be colored or transparent, the color of a given pixelmay be made from any one or a combination of the color layers (e.g.,cyan, magenta, yellow, black) at the full address resolution of thedisplay. When all colorant layers 405, 407, 409 for a pixel are madetransparent, then the pixel shows the background substrate 303 (e.g.,white). Such a display offers the benefit of three or more timesresolution over present matrix LCD devices having the same pixel densitybut that rely on single layer mosaic color. Details of the fabricationof the display are set forth in the above-mentioned co-pendingapplication.

The color to be set for each pixel is addressed by applying a voltageacross the electrodes directly adjacent to the selected color layer. Forexample, assuming yellow is the uppermost colorant layer 405, magenta isthe next colorant layer 407, and cyan is the third colorant layer 409,then pixels in the yellow layer are addressed through row electrodes 401and column electrodes 402, magenta through column electrodes 402 and rowelectrodes 403, and cyan through row electrodes 403 and columnelectrodes 404. This simple common electrode-addressing scheme is madepossible because each colorant molecule is color stable in the absenceof an applied electric field.

FIG. 5 depicts a third embodiment, which employs scan-addressing ratherthan matrix-addressing. Matrix address displays are presently limited inresolution by the number of address lines and spaces that may bepatterned over the relatively large two-dimensional surface of adisplay, each line connecting pixel row or column to the outer edge ofthe display area. In this third embodiment, the bi-stable molecularcolorant layer 301 and background substrate 303 layer construction iscombined with a scanning electrode array printhead to provide a scanningelectrode display apparatus 500 having the same readability benefits asthe first two embodiments described above, with the addition ofcommercial publishing resolution. Scanning electrode arrays and driveelectronics are common to electrostatic printers and their constructionsand interfaces are well-known. Basically, remembering that the bi-stablemolecular switch does not require a holding field, the scanningelectrode array display apparatus 500 changes a displayed image byprinting a pixel row at a time. The scanning electrode array displayapparatus 500 thus provides far greater resolution by virtue of theability to alternate odd and even electrode address lines along opposingsides of the array, to include multiple address layers with pass-througharray connections and to stagger multiple arrays that proportionatelysuperimpose during a scan. The colorant layer 301 may again be patternedwith a color mosaic to produce an exceptionally high resolution scanningcolor display.

More specifically, the third embodiment as shown in FIG. 5 comprises adisplay screen 502, a scanned electrode array 504, and array translationmechanism 501 to accurately move the electrode array across the surfaceof the screen. The display screen 502 again comprises a backgroundsubstrate 303, a transparent view-through layer 305, and at least onebi-stable molecule colorant layer 301. The colorant layer 301 mayinclude a homogeneous monochrome colorant (e.g., black) or color mosaic,as described herein above. The scanned electrode array 504 comprises alinear array or equivalent staggered array of electrodes in contact ornear contact with the background substrate 303. A staggered array ofelectrodes may be used, for example, to minimize field crosstalk betweenotherwise adjacent electrodes and to increase display resolution.

In operation, each electrode is sized, positioned, and electricallyaddressed to provide an appropriate electric field, represented by thearrow labeled “E”, across the colorant layer 301 at a given pixellocation along a pixel column. The field E may be oriented perpendicularto the plane of the colorant layer 301 or parallel to it, depending onthe color switching axis of the colorant molecules. A perpendicularfield may be produced by placing a common electrode (e.g., an ITO layer)on the opposing coating side to the electrode array. The electrode arraymay also be constructed to emit fringe fields; a parallel fringe fieldmay be produced by placing a common electrode adjacent and parallel tothe array. A perpendicular fringe field may be produced by placingsymmetrically spaced parallel common electrodes about the electrodearray(s). The voltage is adjusted so that the dominant field line formeddirectly beneath the array 504 is sufficiently strong to switch theaddressed colorant molecule(s) and divided return lines are not.Additional information regarding alternate embodiments and scanningmechanisms are discussed in the above-mentioned co-pending application.

Present Teachings

The present disclosure relates generally to electronic and opticaldevices whose functional length scales are measured in nanometers, orlarger and, more particularly, to classes of molecules that provide bothelectronic and optical switching. The electronic and/or optical devicesboth of micrometer and nanometer scale may be constructed in accordancewith the teachings herein.

In the parent application to the present application, a molecular systemis disclosed and claimed provided for nanometer-scale reversibleelectronic and optical switches, specifically, electric field-activatedmolecular switches that have an electric field induced band gap changethat occurs via a molecular conformation change or a tautomerization.Changing of extended conjugation via chemical bonding change to changethe band gap is accomplished by providing the molecular system with onerotating portion (rotor) and two or more stationary portions (stators),between which the rotor is attached. In this case, one of the statorscould be a substrate, to which a rotor is directly attached, such as bya linear coupler, which could rotate or not with the rotor.

The molecular system of the parent application, described below withreference to FIG. 6, has three branches (first, second, and thirdbranches) with one end of each branch connected to a junction unit toform a “Y” configuration. The first and second branches are on one sideof the junction unit and the third branch is on the opposite side of thejunction unit. The first branch contains a first stator unit in itsbackbone, the junction unit comprises a second stator unit, and thefirst branch further contains a rotor unit in its backbone between thefirst stator unit and the second stator unit. The rotor unit rotatesbetween two states as a function of an externally applied field. Thesecond branch includes an insulating supporting group in its backbonefor providing a length of the second branch substantially equal to thatof the first branch.

As in the parent application, the embodiments herein turn molecules intoactive electronic devices that can be switched with an external electricfield. Where the parent application employs a single rotatable middlesegment (rotor) on one branch, in the present application, the generalidea is to design into the molecules two or more rotatable middlesegments, or rotors, that each have a large dipole moment and that linktwo other portions of the molecule that are immobilized (stators). Underthe influence of an applied electric field, the vector dipole moment ofeach rotor will attempt to align parallel to the direction of theexternal field. The molecule may be designed such that there are inter-and/or intra-molecular forces, such as hydrogen bonding or dipole-dipoleinteractions as well as steric repulsions, that stabilize the rotors inparticular orientations with respect to the stators. In that case, alarge field would be required to cause the rotors to unlatch from theirinitial orientation and rotate with respect to the stators, if thedirection of the applied field is opposite to that of the dipoles of therotors. Once switched into a particular orientation, the molecule wouldremain in that orientation until it is switched out. However, acomponent of the molecule design is that there may be intra-molecularand/or inter-molecular steric repulsion that will prevent the rotorsfrom rotating through a complete 180 degree half cycle. Instead, therotation would be halted by the steric interaction of bulky groups onthe stators and/or rotors at an angle of approximately 10 to 170 degreesfrom the initial orientation. Furthermore, this 10 to 170 degreeorientation would be stabilized by a different set of inter- and/orintra-molecular hydrogen bonds or dipole interactions, and thus latchedinto place even after the applied field is turned off. For switchmolecules, this ability to latch the rotor between two states separatedby approximately 10 to 170 degrees from the stators is important.

For the orientation where the rotors and stators are all co-planar, themolecule is completely conjugated. Thus, the π- or π- and non-bondingelectrons of the molecule are delocalized over the large portion of themolecule. This is an ON state (high conductivity state or optical stateI) for the molecule. In the case where the rotor is rotated by 10 to 170degrees with respect to the stators, the conjugation of the molecule isbroken and the π- or π- and non-bonding electrons of the molecule are nolonger delocalized over the large portion of the molecule. This is theOFF state (low conductivity state or optical state II) of the molecule.Thus, the molecule is reversibly switchable between the ON and OFFstates.

The following requirements must be met:

-   -   The molecule must have two or more rotor segments and three or        more stator segments;    -   In one state of the molecule, there should be delocalized        π-electrons that extend over a large portion of the molecule        (rotors and stators), whereas in the other state, the        π-electrons are localized on the rotors and stators;    -   The connecting unit between rotors and stators can be a single        σ-bond or at least one atom with (1) non-bonding electron(s),        or (2) π-electrons, or (3) π-electrons and non-bonding        electron(s);    -   The non-bonding electrons, or π-electrons, or π-electrons and        non-bonding electron(s) of the rotor(s) and stators can be        localized or delocalized depending on the conformation of the        molecule, while the rotors rotate when activated by an E-field;    -   The conformation(s) of the molecule can be E-field dependent or        bi-stable;    -   The bi-stable state(s) can be achieved by intra- or        inter-molecular forces such as hydrogen bonding, Coulomb force,        van der Waals force, metal ion complex or dipole        inter-stabilization; and    -   The band gap of the molecule will change depending on the degree        of non-bonding electron, or π-electron, or π-electron and        non-bonding electron de-localization of the molecule. This will        control the electrical conductivity of the molecule, as well as        its optical properties (e.g., color and/or index of refraction,        etc.).

The novel bi-modal molecules herein are active elements in electronicand/or optical devices that can be switched with an external electricfield. The general idea is to design into the molecules rotatablesegments (rotors) that have a large dipole moment (see Examples 1 and 2)and that link two other portions of the molecule that are immobilized(stators). Under the influence of an applied electric field, the vectordipole moment of the rotors will attempt to align parallel to thedirection of the external field. However, the molecule is designed suchthat there are inter- and/or intra-molecular forces, such as hydrogenbonding or dipole-dipole interactions as well as steric repulsions, thatstabilize the rotors in particular orientations with respect to thestators. Thus, a large electric field is required to cause the rotors tounlatch from their initial orientation and rotate with respect to thestators.

Once switched into a particular orientation, the molecule will remain inthat orientation until it is switched out. However, a key component ofthe molecule design is that there is a steric or Coulombic repulsionthat will prevent the rotors from rotating through a complete 180 degreehalf cycle. Instead, the rotation is halted by the steric interaction ofbulky groups on the rotor and stators at an optically and/orelectrically significant angle of typically between 10 and 170 degreesfrom the initial orientation. For the purposes of illustration, thisangle is shown as 90 degrees in the present application. Furthermore,this switching orientation may be stabilized by a different set ofinter- and/or intra-molecular hydrogen bonds or dipole interactions, andis thus latched in place even after the applied field is turned off. Forswitch molecules, this ability to latch the rotors between two statesseparated by an optically and/or electrically significant rotation fromthe stators is important.

Further, the molecules may be designed to include the case of no, orlow, activation barrier for fast but volatile switching. In this lattersituation, bi-stability is not required, and the molecule is switchedinto one state by the electric field and relaxes back into its originalstate upon removal of the field (“bi-modal”). In effect, these forms ofthe bi-modal molecules are “self-erasing”. In contrast, with bi-stablemolecules, the molecule remains latched in its state upon removal of thefield (non-volatile switch), and the presence of the activation barrierin that case requires application of an opposite field to switch themolecule back to its previous state.

When the rotors and stators are all co-planar, the molecule is referredto as “more-conjugated”. Thus, the non-bonding electrons, orπ-electrons, or π-electrons and non-bonding electrons of the molecule,are delocalized over a large portion of the molecule. This is referredto as an “ON” state for the molecule, or “red-shifted state” (“opticalstate I”), and/or “high conductive state”. In the case where at leastone of the rotors is rotated out of conjugation with respect to thestators, the conjugation of the molecule is broken and the π- or π- andnon-bonding electrons are localized over smaller portions of themolecule, referred to as “less-conjugated”. This is an “OFF” state ofthe molecule, or “blue-shifted state” (“optical state II”) and/or “lowconductive state”. Thus, the colorant molecule is reversibly switchablebetween at least two different optical states. It will be appreciatedthat while a 90 degree rotation of the rotor is often depicted, therotation in fact may be any angle that alters or changes conjugation, asdiscussed above.

It will be appreciated by those skilled in the art that in the idealcase, when the rotors and stators are completely coplanar, then themolecule is fully conjugated, and when the rotors are rotated at anangle of, say, 90 degrees with respect to the stators, then the moleculeis non-conjugated. However, due to thermal fluctuations, these idealstates are not fully realized, and the molecule is thus referred to asbeing “more-conjugated” (or “high conductive”) in the former case and“less-conjugated” (or “low conductive”) in the latter case. Further, theterms “red-shifted” and “blue-shifted” are not meant to convey anyrelationship to hue, but rather the direction in the electromagneticenergy spectrum of the energy shift of the gap between the HOMO and LUMOstates.

FIG. 6 is a schematic model of the molecular system of the parentapplication, depicting an E-field-induced band gap change via molecularconformation change (rotor/stator type of model). The molecular system30 has three branches 32, 34, 36 (first, second, and third branches)with one end of each branch connected to a junction unit 38 to form a“Y” configuration. The first and second branches 32, 34 are on one sideof the junction unit 38 and the third branch 36 is on the opposite sideof the junction unit. The first branch 32 contains a first stator unit40 in its backbone, the junction unit 38 comprises a second stator unit,and the first branch further contains a rotor 42 unit in its backbonebetween the first stator unit and the second stator unit. The rotor unit42 rotates between two states with respect to the two stator units 38,40 in response to the external electric field applied by electrodes 44,46. The molecular unit 30 may either be directly connected to theelectrodes 44, 46 with connecting units (not shown in FIG. 6) orsuspended between the two electrodes. The second branch 34 includes aninsulating supporting group in its backbone for providing a length ofthe second branch substantially equal to that of the first branch 32.

FIG. 7 is a schematic model of an embodiment of a molecular system ofthe present teachings, depicting an E-field-induced band gap change viamolecular conformation change (rotor/stator type of model). Themolecular system 130 has three branches 132, 134, 136 (first, second,and third branches) with one end of each branch connected to a junctionunit, or connector, 138 to form a “Y” configuration. The first andsecond branches 132, 134 are on one side of the junction unit 138 andthe third branch 136 is on the opposite side of the junction unit. Thefirst branch 132 contains a first stator unit 140 in its backbone, thejunction unit 138 comprises a second stator unit, and the first branchfurther contains a first rotor 142 unit in its backbone between thefirst stator unit and the second stator unit. Likewise, the secondbranch 134 contains a third stator unit 144 in its backbone, thejunction unit 138 comprises the second stator unit, and the secondbranch further contains a second rotor unit 146 in its backbone betweenthe third stator unit and the second stator unit. It will be appreciatedthat there could be more than one rotor unit in a given branch. Bothrotor units 142, 146 rotate between two states with respect to theirassociated two stator units (stator units 138, 140 in the case of thefirst rotor unit 142 and stator units 138, 144 in the case of the secondrotor unit 146) in response to the external electric field applied byelectrodes 44, 46. The molecular unit 30 may either be directlyconnected to the electrodes 44, 46 with connecting units (not shown inFIG. 7, but described below with reference to Example 1b) or suspendedbetween the two electrodes. The two rotor units 142, 146 may be the sameor different. If they are the same, then the molecular system 130 hastwo energy states, caused by the rotation of the rotor units 142, 146from the more-conjugated state into the less-conjugated state or viceversa. If the rotor units 142, 146 are different, then the molecularsystem 130 has three energy states (both rotors in the more-conjugatedstate, one rotor in the less-conjugated state, and both rotors in theless-conjugated state).

The two rotors 142, 146 may be exactly the same with identical switchthresholds (switch at same field strength) or different. The switchthreshold is defined by a combination of factors that includes rotordipole moment and rotational resistance (de-conjugation energy, stericand Coulombic hinderances to rotation).

The number of switch states in a two-rotor “Y” configured moleculedepends on whether the rotors are electrically connected in parallel orserial, whether the rotors have different rotational thresholds andwhether the third (passive) branch 136 is conductive or non-conductive.When the passive branch 136 is conductive and the rotors have differentswitch thresholds, there will always be three switch states, independentof the parallel/serial status of the rotors (off, conductive, moreconductive). If the two rotors have the same switch thresholds and thepassive branch 136 is conductive, then there will always be two switchstates, on and off. If the passive branch 136 is non-conductive, thenthe rotors must be electrically connected in series for there to be anyon switch state, and then there is only two switch states, on and off.

Example 1a is a generic molecular example of the teachings herein. Inthis molecule, a Y configuration, similar to that depicted in FIG. 6, isemployed. However, in place of the insulating branch 34, a second rotoris employed on the second branch, connected between the junction unitand another stator unit.

where:

A is an Acceptor group comprising an electron-withdrawing group selectedfrom the group consisting of: (a) hydrogen, (b) carboxylic acid and itsderivatives, (c) sulfuric acid and its derivatives, (d) phosphoric acidand its derivatives, (e) nitro, (f) cyano, (g) hetero atoms selectedfrom the group consisting of N, O, S, P, F, Cl, and Br, (h) functionalgroups with at least one of the hetero atoms, (i) saturated orunsaturated hydrocarbons, and (j) substituted hydrocarbons;

D is a Donor group comprising an electron-donating group selected fromthe group consisting of: (a) hydrogen, (b) amines, (c) OH, (d) SH, (e)ethers, (f) saturated or unsaturated hydrocarbons, (g) substitutedhydrocarbons, and (h) functional groups with at least one hetero atomselected from the group consisting of B, Si, I, N, O, S, and P, whereinthe Donor group is more electropositive than the Acceptor group;

Rotor₁ and Rotor₂ are independently different geometric rotatablesystems that may be exactly the same with identical switch thresholds(switch at the same field strength) or different and are conjugatingsystems selected from substituted single aromatic or polyaromatichydrocarbons, or conjugated heterocyclic systems, where (1) the aromatichydrocarbon, or substituted aromatic hydrocarbon, can be either a singlering aromatic (i.e., benzene or substituted benzene) or a poly-aromatic(i.e., naphthalene or its derivatives, acenaphthalene or itsderivatives, anthracene or its derivatives, phenanthrene or itsderivatives, benzanthracene or its derivatives, dibenzanthracene or itsderivatives, fluorene or its derivatives, benzofluorene or itsderivatives, fluoranthene or its derivatives, pyrene or its derivatives,benzopyrene or its derivatives, naphthopyrene or its derivatives,chrysene or its derivatives, perylene or its derivatives, benzoperyleneor its derivatives, pentacene or its derivatives, coronene or itsderivatives, tetraphenylene or its derivatives, triphenylene or itsderivatives, decacyclene or its derivatives), and (2) the conjugatedheterocyclic system can be either a single ring heterocycle or a fusedring heterocycle, wherein the single ring heterocycle can either be a5-membered-ring or 6-membered-ring with one or more heteroatoms in thering, where the heteroatom in the aromatic heterocycles can be anoxygen, sulfur, selenium, nitrogen, or phosphor atom and where thesingle ring of 5-membered-heterocycles can be one of following: furanand its derivatives, pyrrole and its derivatives, thiophene and itsderivatives, porphine and its derivatives, pyrazole and its derivatives,imidazole and its derivatives, triazole and its derivatives, isoxazoleand its derivatives, oxadiazole and its derivatives, thiazole and itsderivatives, isothiazole and its derivatives, thiadiazole and itsderivatives and where the single ring of 6-membered-heterocycles can beone of following: pyridine and its derivatives, pyridazine and itsderivatives, pyrimidine and its derivatives, uracil and its derivatives,azauracil and its derivatives, pyrazine and its derivatives, triazineand its derivatives and where the fused ring heterocycles can either a5-membered fused atomic heterocycle or a 6-membered fused aromaticheterocycle, where the 5-membered fused atomic heterocycle group can beone of following: indole and its derivatives, carbazole and itsderivatives, benzofuran and its derivatives, dibenzofuran and itsderivatives, thianaphthene and its derivatives, dibenzothiophene and itsderivatives, indazole and its derivatives, azaindole and itsderivatives, iminostilbene and its derivatives, norharman and itsderivatives, benzimidazole and its derivatives, benzotriazole and itsderivatives, benzisoxazole and its derivatives, anthranil and itsderivatives, benzoxazole and its derivatives, benzothiazole and itsderivatives, triazolopyrimidine and its derivatives, triazolopyridineand its derivatives, benzselenazole and its derivatives, purine and itsderivatives, etc., and where the 6-membered fused atomic heterocyclegroup can be one of following: quinoline and its derivatives, and itsderivatives, benzoquinoline and its derivatives, acridine and itsderivatives, iso quinoline and its derivatives, benzacridine and itsderivatives, phenathridine and its derivatives, phenanthroline and itsderivatives, phenazine and its derivatives, quinoxaline and itsderivatives, etc.; and

Stator₁, Stator₂, Stator₃, and Connector are different geometric fixedconjugating systems selected from the group consisting of: (a) saturatedor unsaturated hydrocarbons and (b) substituted hydrocarbons, whereinthe hydrocarbon units contain conjugated rings that contribute to anextended conjugation of the molecular system when it is in a planarstate (red shifted state), wherein the stators optionally contain atleast one bridging group, at least one spacing group, or both, whereinthe at least one bridging group is either (a) selected from the groupconsisting of acetylene, ethylene, amide, imide, imine, and azo and isused to connect the stators to the rotors or to connect two or moreconjugated rings to achieve a desired optical property, electricalproperty, or both or (b) selected from the group consisting of a singleatom bridge and a direct sigma bond between the rotors and the statorsand wherein the at least one spacing group is selected from the groupconsisting of phenyl, isopropyl, and tert-butyl and is used to providean appropriate 3-dimensional scaffolding to allow molecular systems topack together while providing space for each rotor to rotate over adesired range of motion.

It will be appreciated that the element labeled “connector” above mayalso be considered to be a stator with three branches thereon. Further,it will be appreciated that Stator 1, Stator 2, Stator 3 may or may notinclude connecting groups CG thereon, depending on the specificapplication.

The moiety A-D in the examples herein forms a dipole having a dipolemoment, which responds to the external E-field by rotating from oneenergy state to another state, as described above with regard torotation of the rotors.

Example 1b below is a real molecular example of this embodiment.

where:

A is the Acceptor group;

D is the Donor group; and

CG are optional connecting units between one molecule and anothermolecule or between a molecule and the solid substrate. They can be asingle connecting unit or multiple connecting units. They may be any oneof the following: hydrogen (utilizing a hydrogen bond), multivalenthetero atoms (i.e., C, N, O, S, P, etc.), functional groups containingthese hetero atoms (e.g., NH, PH, etc.), hydrocarbons (either saturatedor unsaturated), or substituted hydrocarbons.

In Example 1b above, the horizontal dashed lines represent othermolecules or solid substrates (which can be either electrode ornon-electrode depends on applications) to which the molecule isoptionally linked. The direction of the switching field is perpendicularto the horizontal dotted lines. Alternatively, the linking moieties (CG)may be eliminated, and the molecule may be simply placed between the twoelectrodes. The molecule shown above (Example 1b) has been designed withthe internal rotors in a 30 to 70 degree angle to the orientation axisof the entire molecule. In this case, the external field is appliedalong the orientation axis of the molecule as pictured—the electrodes(horizontal dashed lines) are oriented perpendicular to the plane of thepaper and in a 30 to 70 degree angle to the orientation axis of themolecule. Application of an electric field oriented from top to bottomin the diagrams will cause the rotors to rotate such that they are, inone position, more coplanar with the rest of the molecule or, in theother position, less coplanar with the rest of the molecule. In thelatter case, where the rotors are not coplanar with the rest of themolecule, this is the “OFF state” of the molecule, whereas where therotors are coplanar with the rest of the molecule, this is the “ONstate” of the molecule.

The foregoing description assumes that both rotors are identical. Suchan ON/OFF switch is particularly useful for electrical switches, such asused in memory or logic devices, or for switching between two colors (orbetween transparent and one color).

When the molecule depicted in Example 1b is in a less-conjugated state(or “OFF state”), the molecule is less conductive, and its color ischromatically transparent, or blue-shifted in its π-system “localizedstate”. In the more conjugated state (“ON state”), the moleculeevidences high conductivity, and the color of the molecule isred-shifted.

In the case where the rotors are not identical, then intermediateenergetic states become possible. Where there are more than twoenergetic states, a different color may be associated with each state,thereby giving rise to the possibility of creating colored displays.

For the molecules of Example 1b, a single monolayer molecular film isgrown, for example, using Langmuir-Blodgett techniques or self-assembledmonolayers, such that the orientation axis of the molecules isperpendicular to the plane of the electrodes used to switch themolecules. Electrodes may be deposited in the manner described byCollier et al, supra, or methods described in the above-referencedpatent applications. Alternate thicker film deposition techniquesinclude vapor phase deposition, contact or ink-jet printing, or silkscreening.

FIG. 8 is a schematic model of another embodiment of a molecular systemof the present teachings, depicting an E-field-induced band gap changevia molecular conformation change (rotor/stator type of model). Themolecular system 230 has four branches 232, 234, 236, 237 (first,second, third, and fourth branches) with one end of each branchconnected to a junction unit 238 to form an “X” configuration. The firstand second branches 232, 234 are on one side of the junction unit 238and the third and fourth branches 236, 237 are on the opposite side ofthe junction unit. Each branch contains a stator unit in its backbone,the junction unit 238 comprises a second stator unit, and each branchcontains a rotor unit in its backbone between the stator unit and thejunction unit. For branch 232, the rotor 242 is between the stator units238, 240; for branch 234, the rotor 246 is between the stator units 238,244; for branch 236, the rotor 250 is between the stator units 238, 248;and for branch 237, the rotor 254 is between the stator units 238 and252. It will be appreciated that there could be more than one rotor unitin a given branch. Each rotor unit rotates between two states withrespect to its associated two stator units in response to the externalelectric field applied by electrodes 44, 46. The molecular unit 230 mayeither be directly connected to the electrodes 44, 46 with connectingunits (not shown in FIG. 8, but described below with reference toExample 2b) or suspended between the two electrodes. The four rotorunits 242, 246, 250, 254 may be the same or different. If they are thesame, then the molecular system 230 has two energy states, caused by therotation of the rotor units 242, 246, 250, 254 into the more fullyconjugated state or into the less conjugated state. If the rotor units242, 246, 250, 254 are different, then the molecular system 230 has atleast four possible energy states: four energy states for electricalswitching (OFF—all rotors off; conductive—two rotors, each on oppositesides of the junction unit 238, on; more conductive—three rotors on; andyet more conductive—four rotors on) and five states for opticalswitching (most colored—all rotors on; then a different color for eachof the four rotors switching off, rotating in sequence with the addedE-field, assuming each rotor as a different switching energy).

Example 2a is another generic molecular example of the teachings herein.In this molecule, an X configuration is employed. Here, a rotor isplaced on each of the four branches, connected between the junction unitand a stator unit at the end of each branch.

where:

-   -   A is an Acceptor group comprising an electron-withdrawing group        selected from the group consisting of: (a) hydrogen, (b)        carboxylic acid and its derivatives, (c) sulfuric acid and its        derivatives, (d) phosphoric acid and its derivatives, (e)        nitro, (f) cyano, (g) hetero atoms selected from the group        consisting of N, O, S, P, F, Cl, and Br, (h) functional groups        with at least one of the hetero atoms, (i) saturated or        unsaturated hydrocarbons, and (j) substituted hydrocarbons;    -   D is a Donor group comprising an electron-donating group        selected from the group consisting of: (a) hydrogen, (b)        amines, (c) OH, (d) SH, (e) ethers, (f) saturated or unsaturated        hydrocarbons, (g) substituted hydrocarbons, and (h) functional        groups with at least one hetero atom selected from the group        consisting of B, Si, I, N, O, S, and P, wherein the Donor group        is more electropositive than the Acceptor group;    -   Rotor₁ and Rotor₂ are independently different geometric        rotatable systems that may be exactly the same with identical        switch thresholds (switch at the same field strength) or        different and are conjugating systems selected from substituted        single aromatic or polyaromatic hydrocarbons, or conjugated        heterocyclic systems, where (1) the aromatic hydrocarbon, or        substituted aromatic hydrocarbon, can be either a single ring        aromatic (i.e., benzene or substituted benzene) or a        poly-aromatic (i.e., naphthalene or its derivatives,        acenaphthalene or its derivatives, anthracene or its        derivatives, phenanthrene or its derivatives, benzanthracene or        its derivatives, dibenzanthracene or its derivatives, fluorene        or its derivatives, benzofluorene or its derivatives,        fluoranthene or its derivatives, pyrene or its derivatives,        benzopyrene or its derivatives, naphthopyrene or its        derivatives, chrysene or its derivatives, perylene or its        derivatives, benzoperylene or its derivatives, pentacene or its        derivatives, coronene or its derivatives, tetraphenylene or its        derivatives, triphenylene or its derivatives, decacyclene or its        derivatives), and (2) the conjugated heterocyclic system can be        either a single ring heterocycle or a fused ring heterocycle,        wherein the single ring heterocycle can either be a        5-membered-ring or 6-membered-ring with one or more heteroatoms        in the ring, where the heteroatom in the aromatic heterocycles        can be an oxygen, sulfur, selenium, nitrogen, or phosphor atom        and where the single ring of 5-membered-heterocycles can be one        of following: furan and its derivatives, pyrrole and its        derivatives, thiophene and its derivatives, porphine and its        derivatives, pyrazole and its derivatives, imidazole and its        derivatives, triazole and its derivatives, isoxazole and its        derivatives, oxadiazole and its derivatives, thiazole and its        derivatives, isothiazole and its derivatives, thiadiazole and        its derivatives and where the single ring of        6-membered-heterocycles can be one of following: pyridine and        its derivatives, pyridazine and its derivatives, pyrimidine and        its derivatives, uracil and its derivatives, azauracil and its        derivatives, pyrazine and its derivatives, triazine and its        derivatives and where the fused ring heterocycles can either a        5-membered fused atomic heterocycle or a 6-membered fused        aromatic heterocycle, where the 5-membered fused atomic        heterocycle group can be one of following: indole and its        derivatives, carbazole and its derivatives, benzofuran and its        derivatives, dibenzofuran and its derivatives, thianaphthene and        its derivatives, dibenzothiophene and its derivatives, indazole        and its derivatives, azaindole and its derivatives,        iminostilbene and its derivatives, norharman and its        derivatives, benzimidazole and its derivatives, benzotriazole        and its derivatives, benzisoxazole and its derivatives,        anthranil and its derivatives, benzoxazole and its derivatives,        benzothiazole and its derivatives, triazolopyrimidine and its        derivatives, triazolopyridine and its derivatives,        benzselenazole and its derivatives, purine and its derivatives,        etc., and where the 6-membered fused atomic heterocycle group        can be one of following: quinoline and its derivatives, and its        derivatives, benzoquinoline and its derivatives, acridine and        its derivatives, iso quinoline and its derivatives, benzacridine        and its derivatives, phenathridine and its derivatives,        phenanthroline and its derivatives, phenazine and its        derivatives, quinoxaline and its derivatives, etc.; and    -   Stator₁, Stator₂, Stator₃, Stator₄, and Connector are different        geometric fixed conjugating systems selected from the group        consisting of: (a) saturated or unsaturated hydrocarbons and (b)        substituted hydrocarbons, wherein the hydrocarbon units contain        conjugated rings that contribute to an extended conjugation of        the molecular system when it is in a planar state (red shifted        state), wherein the stators optionally contain at least one        bridging group, at least one spacing group, or both, wherein the        at least one bridging group is either (a) selected from the        group consisting of acetylene, ethylene, amide, imide, imine,        and azo and is used to connect the stators to the rotor or to        connect two or more conjugated rings to achieve a desired        optical property, electrical property, or both or (b) selected        from the group consisting of a single atom bridge and a direct        sigma bond between the rotor and the stators and wherein the at        least one spacing group is selected from the group consisting of        phenyl, isopropyl, and tert-butyl and is used to provide an        appropriate 3-dimensional scaffolding to allow molecular systems        to pack together while providing space for each rotor to rotate        over a desired range of motion.

It will be appreciated that the element labeled “connector” above mayalso be considered to be a stator with four branches thereon. Further,it will be appreciated that Stator 1, Stator 2, Stator 3, Stator 4 mayor may not include connecting groups CG thereon, depending on thespecific application.

Example 2b below is a real molecular example of this embodiment.

where:

-   -   A is the Acceptor group;    -   D is the Donor group; and    -   CG are the optional connecting units.

As in Example 1b, electrodes are shown, with which the molecule isassociated, either by direct connection through the CG groups or byvirtue of being suspended between the two electrodes.

The field-switchable molecules of the present disclosure may be used inthe electrical switch and optical switch applications described in FIGS.1-5, as well as in other electrical and optical applications, asmentioned above.

Specifically, a new type of switching mechanism is introduced hereinthat distinguish it from the prior art, namely, an electric field(“E-field”) induced rotation of a rotatable section (rotor) of amolecule to change the band gap of the molecule. The molecule is neveroxidized nor reduced in the toggling of the switch, in contrast to priorart approaches. Also, the part of the molecule that moves is quitesmall, so the switching time is expected to be quite fast. Also, themolecules are much simpler and thus easier and cheaper to make than therotaxanes, catenanes, and related compounds.

The technology disclosed and claimed herein for forming crossed wires(micro-meter or nanometer) may be used to perform a variety of functionsand to form a variety of useful devices and circuits for implementingcomputing on a microscale and even on a nanoscale. For example,applications include molecular wire crossbar memory (U.S. Pat. No.6,128,214), molecular wire crossbar interconnects (MWCI) for signalrouting and communications (U.S. Pat. No. 6,314,019), molecular wirecrossbar memory (U.S. Pat. No. 6,128,214), molecular wire crossbar logic(MWCL) employing programmable logic arrays, a demultiplexer for amolecular wire crossbar network (U.S. Pat. No. 6,256,767), molecularwire transistors (U.S. Pat. No. 6,559,468), and an addressable matrix ofelectrodes for addressing pixels for display purposes (U.S. Pat. No.6,556,470). As illustrated in FIG. 2, for example, the switch 10 can bereplicated in a two-dimensional array to form a plurality, or array, 60of switches to form a crossbar switch 60.

Further, the technology disclosed and claimed herein for forming opticalswitches (micro-meter or nanometer) may be used to assemble displays,electronic books, rewrittable media, electrically tunable opticallenses, electrically controlled tinting for windows and mirrors, opticalcrossbar switches for routing signals from one of many incoming channelsto one of many outgoing channels, and more.

The present teachings provide molecular reversible electronic and/oroptical switches that can be assembled easily to make crossbar and othercircuits. The crossbar circuits have been described in the above-listedseries of patent applications and issued patents. The circuits providememory, logic and communications functions. One example of theelectronic switches is the so-called crossed-wire device, whichcomprises a pair of crossed wires that form a junction where one wirecrosses another at an angle other than zero degrees and at least oneconnector species connecting the pair of crossed wires in the junction.The junction has a functional dimension in nanometers or larger formultilayers. The connector species comprises the molecular systemdisclosed and claimed herein.

The present teachings introduce a new type of switching mechanism,namely, an electric field induced rotation of a rotatable middle section(rotor) of a molecule. Thus, the molecule is neither oxidized norreduced in the toggling of the switch, which avoids the necessity ofbreaking chemical bonds and potentially initiating a nonreversiblereaction. Also, the part of the molecule that moves is quite small, sothe switching time should be very fast. Also, the molecules are muchsimpler and thus easier and cheaper to make than the rotaxanes andrelated compounds.

The devices disclosed herein are generically considered to be electricfield devices, and are to be distinguished from earlier embodiments(described in the above-mentioned related patent applications andpatent) that are directed to electrochemical devices.

The molecular systems disclosed herein are expected to find use in avariety of applications, including, but not limited to, memories, logicdevices, multiplexers, demultiplexers, configurable interconnects forintegrated circuits, field-programmable gate arrays (FGPAs), crossbarswitches, and communication devices, such as cellular phones, mobileappliances, personal digital assistants (PDAs), display, and opticalswitches.

Alternative structures, comprising more than three branches, can also beemployed. For example, a two-sided brush or comb structure may beconstructed having, for example, a backbone parallel to the substratesand multiple (more than four) rotor-containing branches orientednominally orthogonal to the backbone and connecting to the substrates.The backbone could comprise a string of conjugated or non-conjugatedstators, such as a polyphenyl-type structure, for example. In thisinstance, more than four branches are possible within the generalteachings herein.

The concept of a plurality of energetic states for multiple differentrotors was described above. In the general case, an n-rotor system onlyhas up to n+1 possible digital switch states (including all rotorsswitched off). Each rotor will always switch when the E-field is at orabove a threshold defined by the rotor dipole moment. Thus, in theexample of a four rotor system, as the E-field is ramped from zero,there are the following switch states: 0000, 1000, 1100, 1110, 1111(rotors ordered in accordance with minimum switching field). There willlikely be intermediate switch states for partial rotor rotations, bothin color and electrical function.

Industrial Applicability

The field-switchable molecules disclosed herein are expected to find usein micro-scale and nano-scale electronic devices as well as in opticaldevices constructed from micro-scale and even nano-scale components,including a variety of visual displays.

1. A molecular system having at least three branches, with one end ofeach branch connected to an immobile junction unit, with two of saidbranches on one side of said junction unit and with at least one otherbranch on the opposite side of said junction unit, wherein either: saidmolecular system comprises three branches, wherein said two brancheseach contain an immobile stator unit in its backbone, and said twobranches each further contain at least one rotatable rotor unit in itsbackbone between said stator unit and said junction unit; or saidmolecular system comprises four branches, with two of said branches onone side of said junction unit and with two other said branches on theopposite side thereof wherein each branch contains contain an immobilestator unit in its backbone, and each branch further contain a rotatablerotor unit in its backbone between said stator unit and said junctionunit, wherein each rotor unit rotates between two states as a functionof an externally-applied field.
 2. The molecular system of claim 1wherein said molecular system comprises three branches, thereby forminga “Y” configuration.
 3. The molecular system of claim 2 wherein saidthird branch contains a third immobile stator unit in its backbone. 4.The molecular system of claim 2 having the general structure

where: A⁻ is an Acceptor group comprising an electron-withdrawing groupselected from the group consisting of: (a) hydrogen, (b) carboxylic acidand its derivatives, (c) sulfuric acid and its derivatives, (d)phosphoric acid and its derivatives, (e) nitro, (f) cyano, (g) heteroatoms selected from the group consisting of N, O, S, P, F, Cl, and Br,(h) functional groups with at least one of said hetero atoms, (i)saturated or unsaturated hydrocarbons, and (j) substituted hydrocarbons;D⁺ is a Donor group comprising an electron-donating group selected fromthe group consisting of: (a) hydrogen, (b) amines, (c) OH, (d) SH, (e)ethers, (f) saturated or unsaturated hydrocarbons, (g) substitutedhydrocarbons, and (h) functional groups with at least one hetero atomselected from the group consisting of B, Si, I, N, O, S, and P, whereinsaid Donor group is more electropositive than said Acceptor group;Rotor₁ and Rotor₂ are independently different geometric rotatablesystems that may be exactly the same with identical switch thresholds ordifferent and are conjugating systems selected from substituted singlearomatic or polyaromatic hydrocarbons, or conjugated heterocyclicsystems, where (1) the aromatic hydrocarbon, or substituted aromatichydrocarbon, can be either a single ring aromatic or a poly-aromatic and(2) the conjugated heterocyclic system can be either a single ringheterocycle or a fused ring heterocycle; and Stator₁, Stator₂, Stator₃,and Connector are different geometric fixed conjugating systems selectedfrom the group consisting of: (a) saturated or unsaturated hydrocarbonsand (b) substituted hydrocarbons, wherein said hydrocarbon units containconjugated rings that contribute to an extended conjugation of saidmolecular system when it is in a planar state (red shifted state),wherein said stators optionally contain at least one bridging groupG_(n) at least one spacing group R_(n), or both, wherein said at leastone bridging group is either (a) selected from the group consisting ofacetylene, ethylene, amide, imide, imine, and azo and is used to connectsaid stators to said rotor or to connect two or more conjugated rings toachieve a desired optical property, electrical property, or both or (b)selected from the group consisting of a single atom bridge and a directsigma bond between said rotor and said stators and wherein said at leastone spacing group is selected from the group consisting of phenyl,isopropyl, and tert-butyl and is used to provide an appropriate3-dimensional scaffolding to allow molecular systems to pack togetherwhile providing space for each rotor to rotate over a desired range ofmotion.
 5. The molecular system of claim 4 having the formula

where: A is said Acceptor group; D is said Donor group; and CG are saidoptional connecting units.
 6. The molecular system of claim 1 whereinsaid molecular system comprises four branches, thereby forming an “X”configuration.
 7. The molecular system of claim 6 having the generalstructure

where: A⁻ is an Acceptor group comprising an electron-withdrawing groupselected from the group consisting of: (a) hydrogen, (b) carboxylic acidand its derivatives, (c) sulfuric acid and its derivatives, (d)phosphoric acid and its derivatives, (e) nitro, (f) cyano, (g) heteroatoms selected from the group consisting of N, O, S, P, F, Cl, and Br,(h) functional groups with at least one of said hetero atoms, (i)saturated or unsaturated hydrocarbons, and (j) substituted hydrocarbons;D⁺ is a Donor group comprising an electron-donating group selected fromthe group consisting of: (a) hydrogen, (b) amines, (c) OH, (d) SH, (e)ethers, (f) saturated or unsaturated hydrocarbons, (g) substitutedhydrocarbons, and (h) functional groups with at least one hetero atomselected from the group consisting of B, Si, I, N, O, S, and P, whereinsaid Donor group is more electropositive than said Acceptor group;Rotor₁ and Rotor₂ are independently different geometric rotatablesystems that may be exactly the same with identical switch thresholds ordifferent and are conjugating systems selected from substituted singlearomatic or polyaromatic hydrocarbons, or conjugated heterocyclicsystems, where (1) the aromatic hydrocarbon, or substituted aromatichydrocarbon, can be either a single ring aromatic or a poly-aromatic and(2) the conjugated heterocyclic system can be either a single ringheterocycle or a fused ring heterocycle; and Stator₁, Stator₂, Stator₃,Stator₄, and Connector are different geometric fixed conjugating systemsselected from the group consisting of: (a) saturated or unsaturatedhydrocarbons and (b) substituted hydrocarbons, wherein said hydrocarbonunits contain conjugated rings that contribute to an extendedconjugation of said molecular system when it is in a planar state (redshifted state), wherein said stators optionally contain at least onebridging group G_(n) at least one spacing group R_(n), or both, whereinsaid at least one bridging group is either (a) selected from the groupconsisting of acetylene, ethylene, amide, imide, imine, and azo and isused to connect said stators to said rotor or to connect two or moreconjugated rings to achieve a desired optical property, electricalproperty, or both or (b) selected from the group consisting of a singleatom bridge and a direct sigma bond between said rotor and said statorsand wherein said at least one spacing group is selected from the groupconsisting of phenyl, isopropyl, and tert-butyl and is used to providean appropriate 3-dimensional scaffolding to allow molecular systems topack together while providing space for each rotor to rotate over adesired range of motion.
 8. The molecular system of claim 7 having theformula

where: A⁻ is said Acceptor group; D⁺ is said Donor group; and CG aresaid optional connecting units.
 9. The molecular system of claim 1wherein at least some of said rotors have the same dipole moment. 10.The molecular system of claim 9 wherein all said rotors have the samedipole moment.
 11. The molecular system of claim 1 wherein all saidrotors have different dipole moments from each other.
 12. The molecularsystem of claim 1 wherein each said branch further contains at least oneconnecting unit at its terminus, said connecting unit for connectingsaid molecular system to other said molecular systems or to substrates.13. The molecular system of claim 1 wherein each said branch furtherincludes at least one moiety selected from the group consisting of atleast one bridging group and at least one spacing group, said at leastone bridging group for connecting a stator to a rotor or to connect atleast two conjugated rings to achieve a desired effect selected from thegroup consisting of electrical effects and optical effects and said atleast one spacing group for providing a three-dimensional scaffolding toallow said molecular system to pack together with other said molecularsystems while providing space for each rotor to rotate over a desiredrange of motion.
 14. The molecular system of claim 1 wherein said twobranches are each connected to a first electrode and wherein said atleast one other branch is connected to a second electrode, to which saidexternally-applied electric field is connected, thereby forming anelectrical switch.
 15. The molecular system of claim 1 wherein saidmolecular system is suspended between two electrodes such that said twobranches are each electrically associated with a first electrode andwherein said at least one other branch is electrically associated with asecond electrode, to which said externally-applied electric field isconnected, thereby forming an optical switch.
 16. A multi-stablemolecular mechanical device comprising a molecular system configuredwithin an electric field generated by a pair of electrodes andelectrically connected thereto, said molecular system having at leastthree branches, with one end of each branch connected to an immobilejunction unit, with two of said branches on one side of said junctionunit and with at least one other branch on the opposite side of saidjunction unit, wherein either: said molecular system comprises threebranches, wherein said two branches each contain an immobile stator unitin its backbone, and said two branches each further contain at least onerotatable rotor unit in its backbone between said stator unit and saidjunction unit; or said molecular system comprises four branches, withtwo of said branches on one side of said junction unit and with twoother said branches on the opposite side thereof wherein each branchcontains contain an immobile stator unit in its backbone, and eachbranch further contain at least one rotatable rotor unit in its backbonebetween said stator unit and said junction unit, wherein each rotorportion rotates with respect to its associated stator portions betweenat least two different states upon application of said electric field,thereby inducing a band gap change in said molecular system, wherein ina first state, there is extended conjugation over at least most of saidmolecular system, resulting in a relatively smaller band gap, andwherein in a second state, said extended conjugation is changed,resulting in a relatively larger band gap, and wherein in intermediatestates, said conjugation is intermediate between that of said firststate and that of said second state.
 17. The molecular device of claim16 wherein said molecular system comprises three branches, therebyforming a “Y” configuration.
 18. The molecular device of claim 17wherein said third branch contains a third immobile stator unit in itsbackbone.
 19. The molecular device of claim 17 having the generalstructure

where: A⁻ is an Acceptor group comprising an electron-withdrawing groupselected from the group consisting of: (a) hydrogen, (b) carboxylic acidand its derivatives, (c) sulfuric acid and its derivatives, (d)phosphoric acid and its derivatives, (e) nitro, (f) cyano, (g) heteroatoms selected from the group consisting of N, O, S, P, F, Cl, and Br,(h) functional groups with at least one of said hetero atoms, (i)saturated or unsaturated hydrocarbons, and (j) substituted hydrocarbons;D⁺ is a Donor group comprising an electron-donating group selected fromthe group consisting of: (a) hydrogen, (b) amines, (c) OH, (d) SH, (e)ethers, (f) saturated or unsaturated hydrocarbons, (g) substitutedhydrocarbons, and (h) functional groups with at least one hetero atomselected from the group consisting of B, Si, I, N, O, S, and P, whereinsaid Donor group is more electropositive than said Acceptor group;Rotor₁ and Rotor₂ are independently different geometric rotatablesystems that may be exactly the same with identical switch thresholds ordifferent and are conjugating systems selected from substituted singlearomatic or polyaromatic hydrocarbons, or conjugated heterocyclicsystems, where (1) the aromatic hydrocarbon, or substituted aromatichydrocarbon, can be either a single ring aromatic or a poly-aromatic and(2) the conjugated heterocyclic system can be either a single ringheterocycle or a fused ring heterocycle; and Stator₁, Stator₂, Stator₃,and Connector are different geometric fixed conjugating systems selectedfrom the group consisting of: (a) saturated or unsaturated hydrocarbonsand (b) substituted hydrocarbons, wherein said hydrocarbon units containconjugated rings that contribute to an extended conjugation of saidmolecular system when it is in a planar state (red shifted state),wherein said stators optionally contain at least one bridging groupG_(n) at least one spacing group R_(n), or both, wherein said at leastone bridging group is either (a) selected from the group consisting ofacetylene, ethylene, amide, imide, imine, and azo and is used to connectsaid stators to said rotor or to connect two or more conjugated rings toachieve a desired optical property, electrical property, or both or (b)selected from the group consisting of a single atom bridge and a directsigma bond between said rotor and said stators and wherein said at leastone spacing group is selected from the group consisting of phenyl,isopropyl, and tert-butyl and is used to provide an appropriate3-dimensional scaffolding to allow molecular systems to pack togetherwhile providing space for each rotor to rotate over a desired range ofmotion.
 20. The molecular device of claim 19 having the formula

where: A⁻ is said Acceptor group; D⁺ is said Donor group; and CG aresaid optional connecting units.
 21. The molecular device of claim 16wherein said molecular system comprises four branches, thereby formingan “X” configuration.
 22. The molecular device of claim 21 having thegeneral structure

where: A⁻ is an Acceptor group comprising an electron-withdrawing groupselected from the group consisting of: (a) hydrogen, (b) carboxylic acidand its derivatives, (c) sulfuric acid and its derivatives, (d)phosphoric acid and its derivatives, (e) nitro, (f) cyano, (g) heteroatoms selected from the group consisting of N, O, S, P, F, Cl, and Br,(h) functional groups with at least one of said hetero atoms, (i)saturated or unsaturated hydrocarbons, and (j) substituted hydrocarbons;D⁺ is a Donor group comprising an electron-donating group selected fromthe group consisting of: (a) hydrogen, (b) amines, (c) OH, (d) SH, (e)ethers, (f) saturated or unsaturated hydrocarbons, (g) substitutedhydrocarbons, and (h) functional groups with at least one hetero atomselected from the group consisting of B, Si, I, N, O, S, and P, whereinsaid Donor group is more electropositive than said Acceptor group;Rotor₁ and Rotor₂ are independently different geometric rotatablesystems that may be exactly the same with identical switch thresholds ordifferent and are conjugating systems selected from substituted singlearomatic or polyaromatic hydrocarbons, or conjugated heterocyclicsystems, where (1) the aromatic hydrocarbon, or substituted aromatichydrocarbon, can be either a single ring aromatic or a poly-aromatic and(2) the conjugated heterocyclic system can be either a single ringheterocycle or a fused ring heterocycle; and Stator₁, Stator₂, Stator₃,Stator₄, and Connector are different geometric fixed conjugating systemsselected from the group consisting of: (a) saturated or unsaturatedhydrocarbons and (b) substituted hydrocarbons, wherein said hydrocarbonunits contain conjugated rings that contribute to an extendedconjugation of said molecular system when it is in a planar state (redshifted state), wherein said stators optionally contain at least onebridging group G_(n) at least one spacing group R_(n), or both, whereinsaid at least one bridging group is either (a) selected from the groupconsisting of acetylene, ethylene, amide, imide, imine, and azo and isused to connect said stators to said rotor or to connect two or moreconjugated rings to achieve a desired optical property, electricalproperty, or both or (b) selected from the group consisting of a singleatom bridge and a direct sigma bond between said rotor and said statorsand wherein said at least one spacing group is selected from the groupconsisting of phenyl, isopropyl, and tert-butyl and is used to providean appropriate 3-dimensional scaffolding to allow molecular systems topack together while providing space for each rotor to rotate over adesired range of motion.
 23. The molecular device of claim 22 having theformula

where: A⁻ is said Acceptor group; D⁺ is said Donor group; and CG aresaid optional connecting units.
 24. The molecular device of claim 16wherein at least some of said rotors have the same dipole moment. 25.The molecular device of claim 24 wherein all said rotors have the samedipole moment.
 26. The molecular device of claim 16 wherein all saidrotors have different dipole moments from each other.
 27. The moleculardevice of claim 16 wherein each said branch further contains at leastone connecting unit at its terminus, said connecting units forconnecting said molecular system to other said molecular systems or tosubstrates.
 28. The molecular device of claim 16 wherein each saidbranch further includes at least one moiety selected from the groupconsisting of at least one bridging group and at least one spacinggroup, said at least one bridging group for connecting a stator to arotor or to connect at least two conjugated rings to achieve a desiredeffect selected from the group consisting of electrical effects andoptical effects and said at least one spacing group for providing athree-dimensional scaffolding to allow said molecular system to packtogether with other said molecular systems while providing space foreach rotor to rotate over a desired range of motion.
 29. The moleculardevice of claim 16 comprising a crossed-wire device comprising a pair ofcrossed wires that form a junction where one wire crosses another at anangle other than zero degrees and at least one connector speciesconnecting said pair of crossed wires in said junction, said junctionhaving a functional dimension in nanometers, wherein said at least oneconnector species comprises said molecular system.
 30. The moleculardevice of claim 29 wherein said crossed-wire device is selected from thegroup consisting of memories, logic devices, multiplexers,demultiplexers, configurable interconnects for integrated circuits,field-programmable gate arrays (FGPAs), crossbar switches, andcommunication devices.
 31. The molecular device of claim 16 wherein saidmolecular system is connected to said pair of electrodes by connectorunits.
 32. An electric field-activated optical switch comprising amolecular system configured within an electric field generated by a pairof electrodes, said molecular system having at least three branches withone end of each branch connected to an immobile junction unit, with twoof said branches on one side of said junction unit and with at least oneother branch on the opposite side of said junction unit wherein: saidmolecular system comprises three branches, wherein said two brancheseach contain an immobile stator unit in its backbone, and said twobranches each further contain a rotatable rotor unit in its backbonebetween said stator unit and said junction unit; or said molecularsystem comprises four branches, with two of said branches on one side ofsaid junction unit and with two other said branches on the opposite sidethereof wherein each branch contains contain an immobile stator unit inits backbone, and each branch further contain a rotatable rotor unit inits backbone between said stator unit and said junction unit, whereineach rotor portion rotates with respect to its associated statorportions between at least two different states upon application of saidelectric field, thereby inducing a band gap change in said molecularsystem, wherein in a first state, there is extended conjugation over atleast most of said molecular system, resulting in a relatively smallerband gap, wherein in a second state, said extended conjugation ischanged, resulting in a relatively larger band gap, and wherein in anintermediate state, said conjugation is intermediate between that ofsaid first state and that of said second state.
 33. The optical switchof claim 32 wherein said molecular system comprises three branches,thereby forming a “Y” configuration.
 34. The optical switch of claim 33wherein said third branch contains a third immobile stator unit in itsbackbone.
 35. The optical switch of claim 33 having the generalstructure

where: A⁻ is an Acceptor group comprising an electron-withdrawing groupselected from the group consisting of: (a) hydrogen, (b) carboxylic acidand its derivatives, (c) sulfuric acid and its derivatives, (d)phosphoric acid and its derivatives, (e) nitro, (f) cyano, (g) heteroatoms selected from the group consisting of N, O, S, P, F, Cl, and Br,(h) functional groups with at least one of said hetero atoms, (i)saturated or unsaturated hydrocarbons, and (j) substituted hydrocarbons;D⁺ is a Donor group comprising an electron-donating group selected fromthe group consisting of: (a) hydrogen, (b) amines, (c) OH, (d) SH, (e)ethers, (f) saturated or unsaturated hydrocarbons, (g) substitutedhydrocarbons, and (h) functional groups with at least one hetero atomselected from the group consisting of B, Si, I, N, O, S, and P, whereinsaid Donor group is more electropositive than said Acceptor group;Rotor₁ and Rotor₂ are independently different geometric rotatablesystems that may be exactly the same with identical switch thresholds ordifferent and are conjugating systems selected from substituted singlearomatic or polyaromatic hydrocarbons, or conjugated heterocyclicsystems, where (1) the aromatic hydrocarbon, or substituted aromatichydrocarbon, can be either a single ring aromatic or a poly-aromatic and(2) the conjugated heterocyclic system can be either a single ringheterocycle or a fused ring heterocycle; and Stator₁, Stator₂, Stator₃,and Connector are different geometric fixed conjugating systems selectedfrom the group consisting of: (a) saturated or unsaturated hydrocarbonsand (b) substituted hydrocarbons, wherein said hydrocarbon units containconjugated rings that contribute to an extended conjugation of saidmolecular system when it is in a planar state (red shifted state),wherein said stators optionally contain at least one bridging groupG_(n) at least one spacing group R_(n), or both, wherein said at leastone bridging group is either (a) selected from the group consisting ofacetylene, ethylene, amide, imide, imine, and azo and is used to connectsaid stators to said rotor or to connect two or more conjugated rings toachieve a desired optical property, electrical property, or both or (b)selected from the group consisting of a single atom bridge and a directsigma bond between said rotor and said stators and wherein said at leastone spacing group is selected from the group consisting of phenyl,isopropyl, and tert-butyl and is used to provide an appropriate3-dimensional scaffolding to allow molecular systems to pack togetherwhile providing space for each rotor to rotate over a desired range ofmotion.
 36. The optical switch of claim 35 having the formula

where: A⁻ is said Acceptor group; D⁺ is said Donor group; and CG aresaid optional connecting units.
 37. The optical switch of claim 32wherein said molecular system comprises four branches, thereby formingan “X” configuration.
 38. The optical switch of claim 37 having thegeneral structure

where: A⁻ is an Acceptor group comprising an electron-withdrawing groupselected from the group consisting of: (a) hydrogen, (b) carboxylic acidand its derivatives, (c) sulfuric acid and its derivatives, (d)phosphoric acid and its derivatives, (e) nitro, (f) cyano, (g) heteroatoms selected from the group consisting of N, O, S, P, F, Cl, and Br,(h) functional groups with at least one of said hetero atoms, (i)saturated or unsaturated hydrocarbons, and (j) substituted hydrocarbons;D⁺ is a Donor group comprising an electron-donating group selected fromthe group consisting of: (a) hydrogen, (b) amines, (c) OH, (d) SH, (e)ethers, (f) saturated or unsaturated hydrocarbons, (g) substitutedhydrocarbons, and (h) functional groups with at least one hetero atomselected from the group consisting of B, Si, I, N, O, S, and P, whereinsaid Donor group is more electropositive than said Acceptor group;Rotor₁ and Rotor₂ are independently different geometric rotatablesystems that may be exactly the same with identical switch thresholds ordifferent and are conjugating systems selected from substituted singlearomatic or polyaromatic hydrocarbons, or conjugated heterocyclicsystems, where (1) the aromatic hydrocarbon, or substituted aromatichydrocarbon, can be either a single ring aromatic or a poly-aromatic and(2) the conjugated heterocyclic system can be either a single ringheterocycle or a fused ring heterocycle; and Stator₁, Stator₂, Stator₃,Stator₄, and Connector are different geometric fixed conjugating systemsselected from the group consisting of: (a) saturated or unsaturatedhydrocarbons and (b) substituted hydrocarbons, wherein said hydrocarbonunits contain conjugated rings that contribute to an extendedconjugation of said molecular system when it is in a planar state (redshifted state), wherein said stators optionally contain at least onebridging group G_(n) at least one spacing group R_(n), or both, whereinsaid at least one bridging group is either (a) selected from the groupconsisting of acetylene, ethylene, amide, imide, imine, and azo and isused to connect said stators to said rotor or to connect two or moreconjugated rings to achieve a desired optical property, electricalproperty, or both or (b) selected from the group consisting of a singleatom bridge and a direct sigma bond between said rotor and said statorsand wherein said at least one spacing group is selected from the groupconsisting of phenyl, isopropyl, and tert-butyl and is used to providean appropriate 3-dimensional scaffolding to allow molecular systems topack together while providing space for each rotor to rotate over adesired range of motion.
 39. The optical switch of claim 38 having theformula

where: A⁻ is said Acceptor group; D⁺ is said Donor group; and CG aresaid optional connecting units.
 40. The optical switch of claim 32wherein at least some of said rotors have the same dipole moment. 41.The optical switch of claim 40 wherein all said rotors have the samedipole moment.
 42. The optical switch of claim 32 wherein all saidrotors have different dipole moments from each other.
 43. The opticalswitch of claim 32 wherein each said branch further contain connectingunits at its terminus, said connecting units for connecting saidmolecular system to other said molecular systems or to substrates. 44.The optical switch of claim 32 wherein each said branch further includesat least one moiety selected from the group consisting of at least onebridging group and at least one spacing group, said at least onebridging group for connecting a stator to a rotor or to connect at leasttwo conjugated rings to achieve a desired effect selected from the groupconsisting of electrical effects and optical effects and said at leastone spacing group for providing a three-dimensional scaffolding to allowsaid molecular system to pack together with other said molecular systemswhile providing space for each rotor to rotate over a desired range ofmotion.
 45. The optical switch of claim 32 wherein said molecular systemis suspended between two electrodes such that said two branches are eachelectrically associated with a first electrode and wherein said at leastone other branch is electrically associated with a second electrode, towhich said externally-applied electric field is connected, therebyforming said optical switch.
 46. The optical switch of claim 32 whereinsaid molecular system is bi-stable, which provides a non-volatilecomponent.
 47. The optical switch of claim 32 wherein said molecularsystem has essentially a low activation barrier between different statesto provide a fast, but volatile, switch.
 48. The optical switch of claim32 wherein said molecular system has more than two switchable states,such that optical properties of said molecular system can be tuned byeither continuously by application of a decreasing or increasingelectric field to form a volatile switch or the color is changedabruptly by the application of voltage pulses to a switch with at leastone activation barrier.
 49. The optical switch of claim 32 wherein saidmolecular system changes between a transparent state and at least onecolored state.
 50. The optical switch of claim 32 wherein said molecularsystem changes between one colored state and at least one other coloredstate.
 51. The optical switch of claim 32 wherein said molecular systemchanges between one index of refraction and at least one other index ofrefraction.